Between dispersed phase and dispersion medium is insoluble or hardly soluble. Dispersed phase is also known as internal phase, and is discontinuous phase. Dispersed medium is also known as external phase, and is continuous phase.

For common emulsions, generally, one phase is water phase; other phase is insoluble in water phase, and is known as oil phase.

When internal phase is water phase, and external phase is oil phase, the emulsion is water-in-oil type, indicated by W/O.

When internal phase is oil phase, and external phase is water phase, the emulsion is oil-in-water type, indicated by O/W.

In addition, there are multiple emulsions. Multiple emulsions are divided into two types: (1), W/O/W type; (2), O/W/O type.